This application is based on and claims priority from Japanese Patent Applications: 2000-191739 filed Jun. 26, 2000; 2000-211706, filed Jul. 12, 2000, and 2001-148244, filed May 17, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a voltage regulator of a vehicle AC generator.
2. Description of the Related Art
JP-A-6-276796 discloses a self-excited vehicle AC generator in which field current is supplied to a field coil when a phase voltage or a neutral point voltage of an armature coil becomes higher than a predetermined level. The phase voltage or the neutral point voltage, which is AC voltage, is directly applied to a first comparator of a voltage regulator to start intermittent generation. Thereafter, if the phase voltage becomes higher as the rotation speed of the AC generator increases, the phase voltage is applied to a second comparator through a rectifier to start regular generation.
JP-A-3-215200 or its corresponding U.S. Pat. No. 5,182,511, and PCT national publication 8-503308 or its corresponding U.S. Pat. No. 5,602,470 disclose a circuit that includes a differential amplifier connected to two phase-windings of the armature coil to detect the self-excited voltage even if leak current flows into the armature coil.
However, installation of the differential amplifier may increase the cost and man-hour for manufacturing the AC generator. If leak current flows into the armature coil when the AC generator stops, the above-described arrangement may erroneously recognize a voltage caused by the leak current as the self-excited voltage and supply field current to the field coil. This causes serious battery discharge.
Some of the above publications disclose a bypass resistor connecting a phase-winding and a ground to bypass such leak current to the ground.
However, such a bypass resistor may cause harmful heat generation and useless power consumption.
Each of JP-A-3-215200, JP-A-6-284598 and PCT International Publication 8-503308 discloses a signal detection circuit that detects and amplifies a voltage difference between two phase-coils. This detection circuit can correctly detect the generation start signal even if leak current flows into the armature coil.
However, such a signal detection circuit necessitates complicated wiring arrangement in the AC generator, thereby increasing parts and man-hour for manufacturing the AC generator.
Therefore, a main object of the invention is to provide an improved voltage regulator of a vehicle AC generator that is free from the above-stated problem and simple in construction.
A voltage regulator of a vehicle AC generator according to a feature of the invention includes a switching circuit for supplying field current to the field coil of the AC generator in a controlled manner, a field voltage detecting circuit for detecting field voltage induced in the field coil when the field coil is not supplied with field current, and
a switch control circuit for controlling the switching circuit according to said field voltage.
Therefore, the switching circuit can be controlled according to operation of the AC generator with a simple structure arrangement and without trouble of leak current flowing in the armature coil of the AC generator.
A voltage regulator of a vehicle AC generator according to another feature of the invention includes a field current switching circuit connected to the field coil of the AC generator, a control circuit for controlling a field current switching circuit according to an output voltage of said armature coil, a power circuit for supplying electric power to the control circuit, a power drive circuit for controlling supply of electric power from the power circuit to the control circuit and first means for detecting rotation speed of the AC generator. The power drive circuit supplies electric power to the control circuit if the rotation speed becomes as high as a predetermined speed.
This arrangement does not necessitate a bias resistor connected to a portion of the armature coil to detect a self-excited voltage induced in the armature core. Therefore, power loss caused by the bias resistor is eliminated.
The first means may be formed of a permanent-magnet-rotor fixed to the rotor of the AC generator and a pickup coil, and the power drive circuit may supply electric power to the control circuit for a predetermined duration after output voltage of the pickup coil becomes as high as a predetermined voltage.